1. Field of the Invention
The present invention relates in general to a method of manufacturing a cellulose electrode by growing carbon nanotubes on the surface of a cellulose sheet produced from cellulose fibers and supporting a platinum nano-catalyst thereon using chemical vapor deposition (CVD), and more particularly, to a method of manufacturing a cellulose electrode having a platinum nano-catalyst supported thereon, which includes producing a cellulose sheet from cellulose fibers having a plurality of micropores, directly growing carbon nanotubes on the cellulose sheet, and supporting a platinum nano-catalyst on the carbon nanotubes directly grown on the cellulose sheet, to a cellulose electrode having a platinum catalyst supported thereon, which is manufactured through the above method, and to use of cellulose fibers as fuel cell electrodes.
2. Description of the Related Art
Typically, cellulose fibers are widely used as a lightweight composite material, an adsorption and filtration material, or a reinforcing agent, due to greatly superior intrinsic properties in terms of surface area, porosity, and physical strength. However, research into the use of cellulose fibers as a material for fuel cell electrodes through a series of procedures has not yet been performed domestically or abroad. At present, because carbon paper available as an electrode is manufactured from carbon fibers which are relatively expensive, the development of inexpensive electrode material substitutable therefor is urgent.
Korean Patent Application No. 10-2007-0015801, filed by the present inventors, discloses a technique for using carbon paper as fuel cell electrodes by directly growing carbon nanotubes on the surface of carbon paper and then supporting a platinum nano-catalyst on the carbon nanotubes using CVD. The present invention, which further improves such fuel cell electrodes, is directed to a technique for using a cellulose fiber sheet as a high functional/inexpensive material, which is substitutable for the carbon paper.
Carbon nanotubes have superior electrical conductivity, specific surface area, and hydrogen storage performance, and are expected to be useful as a catalyst support. In particular, use of carbon nanotubes as a support of a platinum catalyst for fuel cell electrodes is preferable. Research into carbon nanotubes to date is mainly concerned with the synthesis thereof, and studies on the application thereof are very poor. Further, attempts to apply carbon nanotubes as a catalyst support are very few. However, because the carbon nanotubes have a specific surface structure, they can prevent the aggregation of metal particles when supported with the metal particles.
A catalyst made of platinum which is a noble metal is mainly used for various hydrogenation and reforming reactions, and exhibits activity superior to other metal catalysts, but is problematic in terms of high preparation costs. Thus, in order to overcome these problems, the size of the platinum particles, which are a catalytic active phase, is minimized on a nano-scale, and platinum is supported in a high dispersion state, whereby platinum should be used in a minimum amount to maximize the number of catalytic active sites. To this end, the surface area of the support that supports the catalyst should be very large, and further, in the supporting procedure, the catalyst particles should not be aggregated on the surface of the support.
Presently, in an electrode manufacturing process, various carbon materials are used as the support for the platinum catalyst, but examples using carbon nanotubes have not yet been introduced. In the case where carbon nanotubes are used as the catalyst support for fuel cell electrodes, the performance of the electrode may be greatly increased thanks to superior properties of the carbon nanotubes, including electrical conductivity, hydrogen storage performance, mechanical strength, and surface area.
In a conventional fuel cell electrode manufacturing process, a so-called ‘pasting method’ for applying a platinum-supported carbon catalyst on carbon paper is adopted. In this procedure, the active sites of the platinum catalyst are disadvantageously blocked with each other. On the other hand, in the case where the carbon nanotubes are directly grown on the surface of the electrode and then platinum is supported, a large surface area of the carbon nanotubes may be used as it is, and all of the platinum catalyst particles supported thereon are not blocked but participate in the reaction, greatly increasing the reactive activity.
To date, there are no examples in which only cellulose fibers are used as a material for fuel cell electrodes. Similarly, US Patent Application Publication No. 2006/0286434 A1 discloses that an electrically conductive carbonaceous material is incorporated into a cellulose matrix to thus prepare a cellulose composite, which is then used to form fuel cell electrodes.
Literature related to the growth of carbon nanotubes on the surface of carbon electrodes for use as fuel cell electrode is as follows. That is, Japanese Patent Application Publication No. 2004-59428A discloses a method of manufacturing carbon nanotube electrodes for use as fuel cell electrodes, which includes dispersing a metal catalyst on a carbon substrate through electrophoresis, spray coating, sputtering or CVD, and synthesizing carbon nanotubes using as a carbon source ethylene, carbon monoxide, carbon dioxide, acetylene, and methane through CVD at 400˜900□, or synthesizing carbon nanotubes using plasma-enhanced CVD.
In addition, PCT Publication No. WO 2006/080702 A1 discloses that a nano composite including carbon nanotubes is prepared and is then used for fuel cell electrodes, thereby greatly increasing performance of the fuel cell. According to the above patent, the carbon nanotubes are synthesized by supporting iron, nickel, cobalt or alloys thereof on carbon cloth or carbon fiber through sputtering, evaporation, CVD, electroplating, or electroless plating, and then supplying a carbon source thereto. As such, DC plasma-enhanced CVD is used so that primary carbon nanotubes and additional carbon nanotubes which are grown in the form of branches on the primary nanotubes are separated from each other by a predetermined interval.
In a search of the literature, no examples are found in which carbon nanotubes are directly grown on a cellulose fiber sheet and then platinum catalyst nanoparticles are highly dispersed thereon, thus obtaining a cellulose electrode, which is used as fuel cell electrodes.